Losses across the world's embattled airlines will exceed the previous forecast of $4.7bn (£2.8bn), the industry's leading body has warned.

"We are going to revise them for the worse because the numbers we have seen in passengers and in freight are not showing any improvement," the managing director of the International Air Transport Association (Iata), Giovanni Bisignani, told Reuters.

"Freight has probably touched the bottom, it is minus 21% [year-on-year] since the last two or three months ... but we do not see any kind of improvement.

"But the passenger [sector], where we generate 90% of our revenues, is still roughly 10% down," he said.

Bisignani said it would take three to four years before revenues recovered to where they were before the financial crisis. The world's airlines lost $8bn between them in 2008.

Bisignani warned that plane manufacturers Boeing and Airbus would see orders for new planes down 30% next year as airlines struggled to find the financing required to augment their fleet.

The warning from Iata follows a series of grim financial results that have underlined the pressure facing airlines.